Electrical energy storage cells are widely used to provide power to electronic, electromechanical, electrochemical, and other useful devices. An electric double layer ultracapacitor, for instance, generally employs a pair of polarizable electrodes that contain carbon particles (e.g., activated carbon) impregnated with a liquid electrolyte. Due to the effective surface area of the particles and the small spacing between the electrodes, large capacitance values may be achieved. Nevertheless, problems remain. For instance, many conventional ultracapacitors are sensitive to high temperatures, which may lead to reduced capacitance and increased equivalent series resistance (“ESR”). As such, a need currently exists for an improved ultracapacitor that can operate at high temperatures and still maintain stable electrical properties.